1. Field of the Invention
The present invention relates to an image display apparatus used in order to allow an observer to observe a two-dimensional image formed by an image forming device, and relates to a head mounted display (HMD) having the image display apparatus incorporated therein and including a frame shaped like glasses to be worn on the head of an observer.
2. Description of the Related Art
A virtual-image display apparatus (image display apparatus) in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device is widely known from JP-A-2006-162767.
Further, a virtual-image display apparatus (image display apparatus) using a hologram diffraction grating, in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device is widely known from JP-A-2007-94175.
A head mounted display that detects an angle at which the head mounted display is tilted from a horizontal level using an attitude sensor, and always holds a display image horizontally by image processing or a control driving device such as a motor is widely known from, for example, JP-A-2000-312319. By using the head mounted display having such a mechanism, even if the head of an observer is tilted, it is possible for the observer to observe a horizontal image.